The present invention relates to an engine, and more particularly, to the structure of an oil-supplying route from an oil pump to an oil control valve in an engine with a variable valve mechanism.
As an engine to be mounted on a vehicle, an engine equipped with a variable valve mechanism for controlling the operation of intake and exhaust valves has been widely used. The variable valve mechanism is a mechanism for changing the maximum valve lift amount and/or the valve timing of the intake valves and/or the exhaust valves. The maximum valve lift amount can be changed by increasing or decreasing the reciprocating stroke of the intake and exhaust valves. Furthermore, the valve timing can be changed by moving the phase of the rotation angle of the camshaft in the advancing direction or in the delaying direction with respect to the rotation angle of the crankshaft. The combustion state and combustion efficiency inside the cylinder can be controlled properly and the exhaust performance and fuel consumption of the engine can be improved by controlling the operation of the intake and exhaust valves using this kind of variable valve mechanism.
As the driving system of the variable valve mechanism, an electric type and a hydraulic type are available. In the electric variable valve mechanism, the variable valve mechanism is driven by an electric motor to control the operation of the intake and exhaust valves. On the other hand, this kind of electric variable valve mechanism has problems in the durability and reliability of the electric motor that operates continuously under a high temperature environment. Furthermore, the structures of the cams and camshaft become complicated, thereby having a problem of high cost. Hence, the hydraulic variable valve mechanism is generally used more than the electric variable valve mechanism under the current circumstances.
In many of hydraulic variable valve mechanisms, after the pressure of oil pressurized by an oil pump is adjusted by an oil control valve (hydraulic control valve, OCV), the oil is introduced into the variable valve mechanism via a camshaft. The pressure of the oil introduced into the variable valve mechanism as described above is controlled by the oil control valve, whereby the operation amount of the variable valve mechanism can be continuously changed and satisfactory controllability can be obtained (for example, refer to JP-A-2013-163973).
In the above-mentioned existing hydraulic variable valve mechanism, for example, a mechanical pump operating interlocked with the crankshaft is used as an oil pump. Furthermore, the oil control valve is built in the cylinder head and disposed in the vicinity of the camshaft. In other words, the entire oil flow passage from the oil pump to the oil control valve is built in the cylinder block and the cylinder head. Hence, the temperature of the oil flowing into the oil control valve is liable to rise, and the controllability of the oil control valve becomes low in some cases.
Moreover, in the case of an engine having two camshafts for driving the respective intake and exhaust valves independently (in other words, an engine equipped with a DOHC intake-exhaust valve mechanism), the engine is provided with an oil passage for supplying oil to the camshaft on the intake side and an oil passage for supplying oil to the camshaft on the exhaust side. Hence, in the case that the related-art oil passages described in JP-A-2013-163973 are used, numerous oil passages are required to be formed inside the cylinder head, whereby the structure of the cylinder head becomes complicated.